Exploration of the IgA1 O-Glycoforms Profile and Pathogenic IgA-Complex Compositions by Mass Spectrometry in IgAN

Background: Higher levels of galactose deficient IgA1 (GdIgA1) and poly-IgA complex are critical in the formation of immunodeposits in IgA nephropathy (IgAN). Previously, we found patients with IgA myeloma (IgAMM) without renal IgA deposition or kidney disease also had higher levels of plasma GdIgA1 undesignedly. We aimed to investigate the key IgA-O glycemic profile and pathogenic IgA-complex compositions in IgA nephropathy by mass spectrum. Methods: Plasma IgA, GdIgA1, CD89 captured poly-IgA1 and IgG-IgA complex in IgAN, IgAMM and healthy controls (HCs) were detected by ELISA. Plasma Poly-IgA1 was detected by Western-blot. The variation in O-glycoforms of IgA1 and compositions of poy-IgA complex were evaluated via mass spectrometry of EThcD-sceHCD and HCD MS/MS fragmentation modes. Results: Levels of IgA, GdIgA1, CD89 captured poly-IgA and IgG-IgA complex were higher in IgAMM patients than those in IgAN. IgA1 O-glycoforms indicated higher abundances of GalNAc/HR and gal-deficence/HR in IgAN and HCs than those in IgAMM group, while the absolute GdIgA1 was higher in IgAMM group. Compositional differences of proteins in poly-IgA varied between groups (67 different proteins in IgAN and IgAMM, 14 in IgAN and HCs). Mean percentages of IgA in poly-IgA complex were 72%, 39.4% and 38.0% in IgAMM, IgAN and HCs, respectively. Relative abundances of C3, APOB-100, AMBP and fibronectin were different among groups. In IgAN, the higher APOB-100 group had heavier renal C3 deposition. AMPB abundances were negatively related to eGFR levels and associated with sever T lesions. Conclusion: Higher levels of GdIgA1 and poly-IgA complex in circulation were found in IgAN and IgA myeloma. Distinct different IgA1 O-glycoforms of IgA1 were shown in IgAN and IgAMM. IgA-APOB-100 or IgA-AMBP complex might play potential pathogenic roles or as biomarkers for IgAN.